Forming of superplastic alloy sheet

ABSTRACT

A method of moulding superplastic alloy sheet material by holding a blank of sheet material, heated to a temperature at which it exhibits superplasticity, adjacent a fluid pressure duct or manifold, and applying fluid pressure to the blank sheet through the duct or manifold to cause the heated sheet to conform to the shape of a mould surface arranged on the side of the sheet remote from the duct or manifold. The fluid pressure manifold may be a heated plate having a plurality of apertures therein.

Swanson FORMING OF SUPERPLASTIC ALLOY SHEET [75] Inventor: Colin John Swanson, Bristol,

England [73] Assignee: ISC Alloys Limited, London,

England [22] Filed: Aug. 15, 1973 [21] Appl. No.: 388,418

[30] Foreign Application Priority Data Aug. 16, 1972 United Kingdom 38246/72 Oct. 2, 1972 United Kingdom 45327/72 [52] US. Cl 72/60; 72/364 [51] Int. Cl B2ld 26/04 [58] Field of Search 72/60, 364; 148/115; 29/421 [56] References Cited UNITED STATES PATENTS 3,340,101 9/1967 Fields, Jr. et a]. 148/115 3,529,458 9/1970 Butler Ct 211. 1 72/60 3,535,766 10/1970 Hymes 29/421 1 Aug. 12, 1975 3,595,060 7/l97l Hundy 72/364 FOREIGN PATENTS OR APPLICATIONS 1,231,428 5/1971 United Kingdom OTHER PUBLICATIONS Superplasticity Enchants Metallurgy; by Walter A. Backofen; pp. 2528 of V0]. 165, No. 24, Dec. 15, 1969; of STEEL.

Primary Examiner-Richard J. Herbst Attorney, Agent, or Firm-Holman & Stern [5 7] ABSTRACT A method of moulding superplastic alloy sheet material by holding a blank of sheet material, heated to a temperature at which it exhibits superplasticity, adjacent a fluid pressure duct or manifold, and applying fluid pressure to the blank sheet through the duct or manifold to cause the heated sheet to conform to the shape of a mould surface arranged on the side of the sheet remote from the duct or manifold. The fluid pressure manifold may be a heated plate having a plurality of apertures therein.

9 Claims, 1 Drawing Figure 1 FORMING OF SUPERPLASTIC ALLOY SHEET This invention relates to the pressure-forming of sheet material composed of superplastic alloys, i.e. those exhibiting an appreciable strain-rate sensitivity.

The phenomenon of superplasticity and some of the alloys which exhibit this property are described in, for example, Journal of Metals, December 1962, pages 914-919 in an article by Underwood entitled A Review of Superplasticity and Related Phenomenon. An example of such a superplastic alloy is one comprising 22% aluminium and 78% zinc and which has been conditioned to be in a superplastic state by means of a suitable heat treatment/cooling/working procedure.

British Pat. Specification No. 1,120,007 describes and claims a process wherein a blank of superplastic alloy sheet material is placed across the opening of an enclosure, i.e. a recess or cavity, so as to form an enclosed space between the sheet blank and the enclosure; the alloy sheet is then caused to conform to the shape of a mould surface within the enclosure by applying a differential fluid pressure across the blank.

The present invention provides a method of moulding superplastic alloy sheet material, comprising: holding a blank of sheet material, heated to a temperature at which it exhibits superplasticity, adjacent a fluid pressure duct or manifold in a substantially fluid-tight manner; and applying fluid pressure to the blank through the said duct or manifold to cause the heated sheet to conform to the shape of a mould surface arranged on the side of the sheet remote from the duct or manifold.

Using this technique the mould surface need not necessarily be within an enclosure as described in British Pat. Specification No. 1,120,007.

Usually the sheet blank will be formed from zinc- /aluminium alloy, with or without minor additions of a third metal, which has been rendered superplastic by means of a heat treatment/cooling/working cycle. Such treatments are described for example in British Pat. Specification No. 1,225,819 published March 24, 1971 and British Pat. Specification 1,297,101 published November 22, 1972.

The blank of sheet material may either be preheated, for example by radiant heaters, at a location remote from the fluid pressure duct or manifold prior to being held adjacent the duct or manifold for forming, or the blank may be heated in situ.

The fluid pressure manifold may be in the form of a heated metal plate having a plurality of apertures therein, through which the fluid pressure may be applied. The fluid pressure is then applied through the apertures in the plate to cause the sheet to conform to the shape of the mould surface which is arranged on the side of the sheet remote from the heated plate.

Where the manifold is a heated metal plate there are preferably three or more apertures in the plate. The plate may be heated by means of electrical heating elements incorporated therein or by means of radiant, for example infra-red, heating.

The blank of sheet material may be held in contact with or in close proximity to the heated plate, and where the blank is held in close proximity to the plate it will be necessary to provide a fluid pressure-tight sealing ring or gasket between the blank and the plate.

The mould surface may also be heated.

The fluid pressure may be suitably applied by means of compressed air.

The sheet is preferably at a temperature of about 240 to 260C during moulding.

The mould surface is suitably made of metal.

The present method has the advantages that the sheet blank may be maintained at a uniform temperature during the moulding operation and that there is very little temperature variation across the face of the blank. In addition, projecting mould surfaces may be employed without the necessity of having these mould surfaces situated within a recess or cavity, which could lead to increased mould costs and to difficulties of removing the moulded sheet from the mould.

Removal of the moulded sheet may also be facilitated by impinging a stream of a suitable cooling fluid, for example cold air or water, on the face of the sheet remote from the mould surface. Alternatively, the moulded sheet may be heated to a temperature above the superplastic temperature range before releasing it.

It may be desirable to move the mould surface away from the moulded sheet after forming and cooling, while keeping the sheet clamped to the manifold, so as to facilitate disengagement of the formed sheet from the mould.

It is thus possible to clamp a pre-heated blank of superplastic alloy sheet material adjacent an airpressure duct or manifold, apply air pressure to force the sheet into conformity with a mould surface, cool the moulded sheet, and then move the mould surface and moulded sheet apart while retaining clamping of the moulded sheet to the duct or manifold. This would be impossible to do by the technique described in British Pat. Specification No. 1,120,007.

A further advantage is that the mould itself is not subjected to clamping pressure so that distortion of the mould due to such pressure cannot occur. Since cast moulds are liable to be porous, clamping of the sheet material against such moulds is liable to lead to ingress of material into the pores of the mould, which leads to difficulty of disengagement of sheet from mould. Thus it is desirable not to clamp the sheet blank to the mould and it is possible to avoid this by means of the present method.

The invention will be further described, by way of example only, with reference to the accompanying drawing which is a schematic side view of an apparatus for moulding superplastic alloy sheet material.

The drawing shows a mould surface 1 against which is to be moulded a blank 2 of superplastic alloy sheet material. The blank 2 is arranged on a fluid pressure manifold comprised by a plate 3 having a plurality of apertures 3a; a radiant heater 4 is placed below the plate 3 for heating the latter. The blank 2 is secured on the plate 3 by means of a set of clamps 5. An air-supply pipe 6 is arranged below the plate 3 but above the heater 4.

The apparatus described above operates as follows.

The sheet blank 2 is heated by contact with plate 3 which is in turn heated by the radiant heater 4. Compressed air is then supplied under pressure through the pipe 6 and causes the heated blank 2 to bulge outwardly and eventually to conform to the shape of the mould surface 1, which is also heated.

In an alternative arrangement, the blank is not clamped against the plate, but is held in close proxim ity; a suitable sealing ring or gasket is then interposed between the blank and the plate.

The plate may be heated by other means, for example by electrical elements incorporated therein or by impinging flames on the surface of the plate.

The fluid pressure manifold comprised by the plate 3 provided with a plurality of apertures 3a may be replaced by a fluid pressure duct, in the latter case there being a single aperture between the compressed air supply and the blank of sheet material.

I claim: 1. A method of moulding superplastic alloy sheet material, comprising: holding a blank of sheet material in a substantially fluid-tight manner on top of and in contact with a plate having a plurality of apertures therein and heated by a heat source remote from the plate; heating the blank to a temperature at which is exhibits superplasticity; and applying fluid pressure to the blank through the apertures in the plate to cause the heated sheet to conform to the shape of a projecting mould surface situated above the sheet.

2. A method as claimed in claim 1 wherein there are at least three apertures in the said plate.

3. A method as claimed in claim 1 comprising heating 5. A method as claimed in claim 1 comprising hold- I ing the blank of sheet material at a temperature of from 240 to 260C during moulding.

6. A method as claimed in claim 1 further comprising releasing the moulding sheet from the mould surface by impinging a stream of cooling fluid on the face of the sheet remote from the mould surface.

7. A method as claimed in claim 6 further comprising moving the mould surface away from the moulded sheet after forming and cooling to disengage the formed sheet from the mould.

8. A method as claimed in claim 1 wherein the superplastic sheet material is a zinc/aluminium alloy containing 78% by weight of zinc and 22% by weight of aluminium.

9. A method as claimed in claim 1 wherein the heat source for heating the plate comprises a radiant heater on the side of the plate remote from the blank of sheet material. 

1. A method of moulding superplastic alloy sheet material, comprising: holding a blank of sheet material in a substantially fluid-tight manner on top of and in contact with a plate having a plurality of apertures therein and heated by a heat source remote from the plate; heating the blank to a temperature at which is exhibits superplasticity; and applying fluid pressure to the blank through the apertures in the plate to cause the heated sheet to conform to the shape of a projecting mould surface situated above the sheet.
 2. A method as claimed in claim 1 wherein there are at least three apertures in the said plate.
 3. A method as claimed in claim 1 comprising heating the mould surface.
 4. A method as claimed in claim 1 wherein the applied pressure fluid is compressed air.
 5. A method as claimed in claim 1 comprising holding the blank of sheet material at a temperature of from 240* to 260*C during moulding.
 6. A method as claimed in claim 1 further comprising releasing the moulding sheet from the mould surface by impinging a stream of cooling fluid on the face of the sheet remote from the mould surface.
 7. A method as claimed in claim 6 further comprising moving the mould surface away from the moulded sheet after forming and cooling to disengage the formed sheet from the mould.
 8. A method as claimed in claim 1 wherein the superplastic sheet material is a zinc/aluminium alloy containing 78% by weight of zinc and 22% by weight of aluminium.
 9. A method as claimed in claim 1 wherein the heat source for heating the plate comprises a radiant heater on the side of the plate remote from the blank of sheet material. 